Fate of chlorothalonil on snowpeas and assessment of its residues in french beans and passion fruits in Nairobi

Abstract

Chlorothalonil (2, 4, 5, 6-tetrachlorophthalonitrile) is a broad spectrum contact fungicide. It has both agricultural and household uses. Residues of chlorothalonil are regularly found on farm produce of plants that are grown using the fungicide. The maximum residue limit (MRL) for chlorothalonil ranges from O.Olmg/Kg in bananas to 70 mg/Kg in chili dry pepper; while the Acceptable Daily Intake (ADI) is 0.03 mg/Kg. In this study, the fate of applied chlorothalonil in soil and snow peas and its residue levels on French beans, passion fruits and snow peas sold in Nairobi were established. Controlled and treated experiments were conducted in a green house on soil obtained from Magumu location of south Kinangop division, Nyandarua District, Central province. Chlorothalonil residues were soxhlet extracted from samples using organic solvents, detected and quantified by Gas Liquid Chromatograph with an Electron Capture Detector and confirmed by Electron Impact Ionisation Gas Chromatograph mass spectrometer (EI-GCMS). Results obtained indicate that chlorothalonil has a dissipation half-life of 2 days in snow peas and 10.2 days in the soil. At a Pre-harvest interval of 21 days chlorothalonil residues measured 0.0126 mg/Kg for snow peas grown on untreated soil and 0.0245 mg/Kg for those grown on treated soil. Both levels were below both EU and Codex MRLs of 5 and 2 mg/Kg respectively and the ADI of 0.03mg/Kg for snow peas. Chlorothalonil residue levels in assessed fruits and vegetables ranged from non-detectable (ND) levels to 0.012 mg/kg in snow peas, ND to 0.021mg/kg in French beans and ND to 0.009 mg/Kg in passion fruits. The experimental Limit of Detection for the method was established to be 0.004 mg/Kg while the Limit of Quantitation was 0.013 mg/Kg. An average enrichment factor of 3.86 was applied during analysis to enable detection and quantitation of residues at low levels. The observed residues did not violate both the EU and Codex MRLs. However, presence ofchlorothalonil residues on passion fruit indicates unauthorized use of the fungicide, indicating potential misuse of pesticides.